Managing secondary cell connections in unlicensed spectrum

ABSTRACT

In wireless communication networks using carrier aggregation including a secondary component carrier in unlicensed spectrum, a user equipment (UE) may monitor a downlink radio link quality of secondary cells for an event indicating failure of a communication link in the unlicensed spectrum with a secondary cell. The UE detects one or more failure events based on the downlink radio link quality. When a designated set of failure events is detected, the UE declares a failure state on the secondary cell. In response to the failure state, the UE may adjust operations related to the secondary component carrier in the unlicensed spectrum in order to save power and resources.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present Application for Patent claims priority to Provisional Application No. 62/357,246 entitled “MANAGING SECONDARY CELL CONNECTIONS IN UNLICENSED SPECTRUM” filed Jun. 30, 2016, which is assigned to the assignee hereof, and incorporated herein by reference in its entirety.

BACKGROUND

Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to managing secondary cell connections.

Background

Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

SUMMARY

The following disclosure presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In one aspect of the disclosure, a method for wireless communication on a secondary component carrier in an unlicensed spectrum in a wireless communication network using carrier aggregation is provided. The method includes monitoring a downlink radio link quality of one or more configured secondary cells operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link with at least one of the configured secondary cells. The method may include detecting a first event based on the downlink radio link quality. The method may include declaring a failure state on the at least one of the configured secondary cells in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.

An additional aspect of the present disclosure is directed to an apparatus for wireless communication on a secondary component carrier in an unlicensed spectrum in a wireless communication network using carrier aggregation. The apparatus may include means for monitoring a downlink radio link quality of one or more configured secondary cells operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link with at least one of the configured secondary cells. The apparatus may include means for detecting a first event based on the downlink radio link quality. The apparatus may include means for declaring a failure state on the at least one of the configured secondary cells in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.

An additional aspect of the present disclosure is directed to a non-transitory computer-readable medium having computer executable code stored thereon. The code includes code for causing a computer to monitor a downlink radio link quality of one or more secondary cells operating in an unlicensed spectrum at a mobile device for an event indicating failure of a communication link with at least one of the configured secondary cells. The code may include code for causing the computer to detect a first event based on the downlink radio link quality. The code may include code for causing the computer to declare a failure state on the at least one of the configured secondary cells in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.

An additional aspect of the present disclosure is directed to an apparatus configured for wireless communication. The apparatus includes at least one processor and a memory coupled to the processor. The processor may be configured to monitor a downlink radio link quality of one or more secondary cells operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link with at least one of the configured secondary cells. The processor may be configured to detect a first event based on the downlink radio link quality. The processor may be configured to declare a failure state on the at least one of the configured secondary cells in response to detecting the first event, during which mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of a mobile communication system.

FIG. 2 is a block diagram conceptually illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure.

FIG. 3 is a block diagram illustrating a wireless network configured according to aspects of the present disclosure.

FIG. 4 is a functional block diagram illustrating example blocks executed to implement aspects of the present disclosure.

FIG. 5 is a timing diagram illustrating a UE configured according to aspects of the present disclosure.

FIG. 6 is a block diagram illustrating a UE configured according to aspects of the present disclosure.

FIG. 7 is a block diagram illustrating a UE including a radio link status component configured according to aspects of the present disclosure.

FIG. 8 illustrates an example of carrier aggregation using a component carrier in unlicensed spectrum according to aspects of the present disclosure.

FIG. 9 illustrates an example of carrier sense adaptive transmission (CSAT) for use in unlicensed spectrum according to aspects of the present disclosure.

FIG. 10 illustrates an example of an enhanced CSAT (eCSAT) system that may operate without a clear channel assessment (CCA) or listen before talk (LBT) procedure according to aspects of the present disclosure.

FIG. 11 illustrates an example of eCSAT operation with a CCA or LBT procedure according to aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology, such as Universal Terrestrial Radio Access (UTRA), Telecommunications Industry Association's (TIA's) CDMA2000®, and the like. The UTRA technology includes Wideband CDMA (WCDMA) and other variants of CDMA. The CDMA2000® technology includes the IS-2000, IS-95 and IS-856 standards from the Electronics Industry Alliance (EIA) and TIA. A TDMA network may implement a radio technology, such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, and the like. The UTRA and E-UTRA technologies are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the “3rd Generation Partnership Project” (3GPP). CDMA2000® and UMB are described in documents from an organization called the “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio access technologies mentioned above, as well as other wireless networks and radio access technologies. For clarity, certain aspects of the techniques are described below for LTE or LTE-A (together referred to in the alternative as “LTE/-A”) and use such LTE/-A terminology in much of the description below.

In some systems, LTE in unlicensed spectrum may be employed in a standalone configuration, with all carriers operating exclusively in an unlicensed portion of the wireless spectrum (e.g., LTE Standalone). In other systems, LTE in unlicensed spectrum may be employed in a manner that is supplemental to licensed band operation by providing one or more unlicensed carriers operating in the unlicensed portion of the wireless spectrum in conjunction with an anchor licensed carrier operating in the licensed portion of the wireless spectrum (e.g., LTE Supplemental DownLink (SDL)). In either case, carrier aggregation may be employed to manage the different component carriers, with one carrier serving as the Primary Cell (PCell) for the corresponding UE (e.g., an anchor licensed carrier in LTE SDL or a designated one of the unlicensed carriers in LTE Standalone) and the remaining carriers serving as respective Secondary Cells (SCells). In this way, the PCell may provide an FDD paired downlink and uplink (licensed or unlicensed), and each SCell may provide additional downlink capacity as desired. Additionally, unlicensed spectrum may also be referred to as a shared spectrum. In an aspect, an unlicensed spectrum may refer to a spectrum in which multiple devices gain access to a medium by contention-based operations.

FIG. 1 shows a wireless network 100 for communication, which may be an LTE-A network operating at least in part in an unlicensed spectrum. The wireless network 100 includes a number of evolved node Bs (eNBs) 110 and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB 110 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in FIG. 1, the eNBs 110 a, 110 b and 110 c are macro eNBs for the macro cells 102 a, 102 b and 102 c, respectively. The eNB 110 x is a pico eNB for a pico cell 102 x, serving a UE 120 x. And, the eNBs 110 y and 110 z are femto eNBs for the femto cells 102 y and 102 z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

The wireless network 100 may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in FIG. 1, a relay station 110 r may communicate with the eNB 110 a and a UE 120 r, in which the relay station 110 r acts as a relay between the two network elements (the eNB 110 a and the UE 120 r) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like.

The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs 120 are dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a smart phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 MHz, respectively.

In LTE/-A, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The eNB may send the PSS, SSS and Physical Broadcast Channel (PBCH) in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the Physical Control Format Indicator Channel (PCFICH) and Physical Hybrid Automatic Repeat Request (HARD) Indicator Channel (PHICH) across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the Physical Downlink Control Channel (PDCCH) to groups of UEs in certain portions of the system bandwidth. The eNB may send the Physical Downlink Shared Channel (PDSCH) to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.

The wireless network 100 uses the diverse set of eNBs 110 (i.e., macro eNBs, pico eNBs, femto eNBs, and relays) to improve the spectral efficiency of the system per unit area. Because the wireless network 100 uses such different eNBs for its spectral coverage, it may also be referred to as a heterogeneous network. The macro eNBs 110 a-c are usually carefully planned and placed by the provider of the wireless network 100. The macro eNBs 110 a-c generally transmit at high power levels (e.g., 5 W-40 W). The pico eNB 110 x and the relay station 110 r, which generally transmit at substantially lower power levels (e.g., 100 mW-2 W), may be deployed in a relatively unplanned manner to eliminate coverage holes in the coverage area provided by the macro eNBs 110 a-c and improve capacity in the hot spots. The femto eNBs 110 y-z, which are typically deployed independently from the wireless network 100 may, nonetheless, be incorporated into the coverage area of the wireless network 100 either as a potential access point to the wireless network 100, if authorized by their administrator(s), or at least as an active and aware eNB that may communicate with the other eNBs 110 of the wireless network 100 to perform resource coordination and coordination of interference management. The femto eNBs 110 y-z typically also transmit at substantially lower power levels (e.g., 100 mW-2 W) than the macro eNBs 110 a-c.

In operation of a heterogeneous network, such as the wireless network 100, each UE is usually served by the eNB 110 with the better signal quality, while the unwanted signals received from the other eNBs 110 are treated as interference. While such operational principals can lead to significantly sub-optimal performance, gains in network performance are realized in the wireless network 100 by using intelligent resource coordination among the eNBs 110, better server selection strategies, and more advanced techniques for efficient interference management.

In deployments of heterogeneous networks, such as the wireless network 100, a UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering eNBs. A dominant interference scenario may occur due to restricted association. For example, in FIG. 1, the UE 120 y may be close to the femto eNB 110 y and may have high received power for the eNB 110 y. However, the UE 120 y may not be able to access the femto eNB 110 y due to restricted association and may then connect to the macro eNB 110 c (as shown in FIG. 1) or to the femto eNB 110 z also with lower received power (not shown in FIG. 1). The UE 120 y may then observe high interference from the femto eNB 110 y on the downlink and may also cause high interference to the eNB 110 y on the uplink. Using coordinated interference management, the eNB 110 c and the femto eNB 110 y may communicate over the backhaul 134 to negotiate resources. In the negotiation, the femto eNB 110 y agrees to cease transmission on one of its channel resources, such that the UE 120 y will not experience as much interference from the femto eNB 110 y as it communicates with the eNB 110 c over that same channel.

FIG. 2 shows a block diagram of a design of a base station/eNB 110 and a UE 120, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, the eNB 110 may be the macro eNB 110 c in FIG. 1, and the UE 120 may be the UE 120 y. The eNB 110 may also be a base station of some other type. The eNB 110 may be equipped with antennas 234 a through 234 t, and the UE 120 may be equipped with antennas 252 a through 252 r.

At the eNB 110, a transmit processor 220 may receive data from a data source 212 and control information from a controller/processor 240. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232 a through 232 t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 232 a through 232 t may be transmitted via the antennas 234 a through 234 t, respectively.

At the UE 120, the antennas 252 a through 252 r may receive the downlink signals from the eNB 110 and may provide received signals to the demodulators (DEMODs) 254 a through 254 r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all the demodulators 254 a through 254 r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 260, and provide decoded control information to a controller/processor 280.

On the uplink, at the UE 120, a transmit processor 264 may receive and process data (e.g., for the PUSCH) from a data source 262 and control information (e.g., for the PUCCH) from the controller/processor 280. The transmit processor 264 may also generate reference symbols for a reference signal. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by the modulators 254 a through 254 r (e.g., for SC-FDM, etc.), and transmitted to the eNB 110. At the eNB 110, the uplink signals from the UE 120 may be received by the antennas 234, processed by the demodulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 120. The processor 238 may provide the decoded data to a data sink 239 and the decoded control information to the controller/processor 240.

The controllers/processors 240 and 280 may direct the operation at the eNB 110 and the UE 120, respectively. The controller/processor 240 and/or other processors and modules at the eNB 110 may perform or direct the execution of various processes for the techniques described herein. The controllers/processor 280 and/or other processors and modules at the UE 120 may also perform or direct the execution of the functional blocks illustrated in FIG. 4, and/or other processes for the techniques described herein. The memories 242 and 282 may store data and program codes for the eNB 110 and the UE 120, respectively. A scheduler 244 may schedule UEs for data transmission on the downlink and/or uplink.

LTE-A UEs use spectrum up to 20 MHz bandwidths allocated in a carrier aggregation of up to a total of 100 MHz (5 component carriers) used for transmission in each direction. Generally, less traffic is transmitted on the uplink than the downlink, so the uplink spectrum allocation may be smaller than the downlink allocation. For example, if 20 MHz is assigned to the uplink, the downlink may be assigned 100 MHz. These asymmetric FDD assignments will conserve spectrum and are a good fit for the typically asymmetric bandwidth utilization by broadband subscribers.

For the LTE-A mobile systems, two types of carrier aggregation (CA) methods have been proposed, continuous CA and non-continuous CA. Non-continuous CA occurs when multiple available component carriers are separated along the frequency band. On the other hand, continuous CA occurs when multiple available component carriers are adjacent to each other. Both non-continuous and continuous CA aggregate multiple LTE/component carriers to serve a single unit of LTE-A UE.

According to various aspects, a UE operating in CA may be configured to aggregate certain functions of multiple carriers, such as control and feedback functions, on the same carrier, which may be referred to as “primary component carriers.” The network entities, eNBs, access points, and the like that communicate with a UE using the primary component carriers are referred to as “primary cells” or “PCells.” The remaining carriers that depend on the primary carrier for support are referred to as “secondary component carriers.” The network entities, eNBs, access points, and the like that communicate with a UE using the secondary component carriers are referred to as “secondary cells” or “SCells.” For example, the UE may aggregate control functions such as those provided by the optional dedicated channel (DCH), the nonscheduled grants, a physical uplink control channel (PUCCH), and/or a physical downlink control channel (PDCCH). Signaling and payload may be transmitted both on the downlink by the eNB to the UE, and on the uplink by the UE to the eNB.

In cellular networks, in particular LTE networks, UEs are expected to monitor the quality of the radio link of the primary cell's received signal. The purpose of radio link monitoring (RLM) in the UE is to monitor the downlink radio link quality of the primary serving cell in a connected state and may be based on the cell specific reference signals (RSs). This, in turn, may enable the UE, when in a connected state, to determine whether the UE is in-sync or out-of-sync with respect to the UE's primary serving cell. In operation, counters may be used to count the consecutive in-sync and out-of-sync indicators, respectively. In case of a the consecutive primary cell out-of-sync counter exceeding a certain number or threshold value, the UE may start a network-configured radio link failure timer. The timer may be stopped prior to expiration if the consecutive in-sync counter records a certain number of consecutive in-sync indications reported by the UE's physical layer. Both the out-of-sync and in-sync counters are typically configured by the network. Upon expiry of the timer, without being stopped by the in-sync counter, Radio Link Failure (RLF) occurs at the UE and, consequently, the UE may start a re-establishment procedure to reestablish the radio communication link.

The UE's estimate of the downlink radio link quality may be compared with out-of-sync and in-sync thresholds for the purpose of RLM. The out-of-sync and in-sync thresholds may be expressed in terms of a Block Error Rate (BLER) of a hypothetical PDCCH transmission from the serving cell. The out-of-sync threshold may correspond to a 10% BLER while the in-sync threshold may correspond to a 2% BLER. The same threshold levels may be applicable with and without discontinuous reception (DRX). The mapping between the cell specific RS-based downlink quality and the hypothetical PDCCH BLER may be a UE implementation design choice.

In the case of carrier aggregation, RLM requirements may only apply to the primary cell and the UE may not perform RLM monitoring of the secondary cells. In other words, when the UE is configured with secondary cells, it may use the primary cell to detect the downlink radio link quality, and for sending out-of-sync/in-sync indications to higher layers. The eNB may determine radio link quality of the secondary cells via a channel quality indicator (CQI) or other such measurement reports.

A UE may operate a demodulation path that includes time/frequency tracking loops that can correct up to a certain amount of time or frequency shift due to multi-path or Doppler shift effect. These tracking loops generally have limited corrective capabilities and may be initialized at the start time of the connection with the associated secondary cell. Without proper initialization, (1) the tracking loops may not converge, or (2) the convergence time may be as high as tens of milliseconds to a few hundreds of milliseconds, which may be many times higher than the typical subframe duration (e.g., 1 ms for LTE).

In the context of carrier aggregation the following situations can occur when a UE is configured with one or more secondary cells: (1) A secondary cell may be activated for a UE when the UE is outside the secondary cell range (or coverage area) and then, moves into the secondary cell range sometime after the activation; (2) A UE temporarily moves out of a secondary cell range and then moves back into the range of the secondary cell when the primary cell/secondary cell timing difference is substantially different from the time where the UE left the secondary cell range (e.g., theoretically up to 62.6 μs, considering the LTE specifications allow for up to 31.3 μs PCell/SCell timing difference), such as, for example, when remote-radio-heads (RRH) are used for secondary cell coverage extensions, etc.; and (3) A secondary cell's RF chain may be relinquished in order to be used to access another wireless technology (opportunistic CA) and is given back to the LTE stack after a long duration of time. For example, a secondary cell's RF chain and demodulation path may be used to tune to the frequency of a cell of another technology (e.g., Simultaneous Voice LTE (SV-LTE), Dual SIM, Dual-Active (DSDA) technologies, etc.). In operation, the UE may stop monitoring the secondary cell to answer another technology call, such as a circuit switched call on a 1× system, and then, sometime later, return to monitoring the secondary cell.

Without active management of the connections with the SCells, during the time that the UE is out of SCell coverage and/or is not able to track time/frequency of the SCell, the state of the tracking loops may become obsolete and may de-converge to random states. Therefore, it may become impossible for the tracking loops to re-converge or the convergence time may become too long once the UE returns to the SCell coverage area. This can be important with respect to time offset of the time tracking loop as the time offset variations between PCell and SCell may be up to 31.3 μs.

When a secondary cell is operating in an unlicensed spectrum, communications may be subject to clear channel assessment (CCA). For example, a secondary cell may mute a transmission when it detects another radio transmission using the unlicensed spectrum. In an aspect, some metrics of secondary cell performance may be affected by the secondary cell muting transmissions. For example, from the perspective of a UE, it is difficult to tell the difference between a transmission in a sub-frame from the secondary cell with a low transmission power and a sub-frame where the secondary cell has muted the transmission. Accordingly, a metric such as a block error rate or SNR may be misleading. For example, a high block error rate or low SNR may occur when the secondary cell is muting transmissions even though the UE may be capable of receiving a signal from the secondary cell when the secondary cell does transmit. In another aspect, a UE may attempt to determine whether the secondary cell transmitted in a sub-frame by monitoring a cell specific reference signal (CRS). If the UE does not detect a CRS in a sub-frame, the UE may exclude the sub-frame from another measurement such as BLER or SNR. However, because it is difficult to determine whether the sub-frame was muted or the radio link was poor quality, excluding the sub-frame may artificially boost some metrics.

Various aspects of the present disclosure provide for monitoring of the link quality between the UE and SCells operating in unlicensed spectrum to detect a failure event. For example, a failure event may include the UE going out of range of an SCell or an SCell being substantially blocked from transmitting by another system. The UE may detect a failure event when a high number of search failures are detected, a low number of non-muted sub-frames are received, no indications of suitable radio link quality are reported, or no acceptable SNR is measured for a time period. When such a failure event is detected, the UE may declare a failure state for the connection with the SCell associated with the failure event. In declaring the failure state, the UE is determining for itself the failed state. For purposes of this application, the UE declaring the failure state with the SCell does not include signaling any network entity outside of the UE that such failure has occurred. The declared failure state is internal to the UE. Based on this failure state, the UE may adjust operations, such as by suspending or deactivating certain components/modules and/or operations associated with the connection to the SCells, modifying the radio frequency (RF) chip state (e.g., disabling the RF chip or placing the RF chip in a lower power mode; disabling transmission while keeping reception enabled, etc.), suspending the transmit and receive paths for the SCell, reducing the power or voltage levels of the device components, changing memory usage or operating frequency of certain device components, and the like. When such failure state is declared, the UE may reduce resource consumption when certain resources associated with maintaining the connection to the associated SCell are not needed.

Also in response to declaring the failure state, the UE may begin a cell search for the SCell. The cell search may be a narrowband search that monitors for PSS/SSS of the SCell. When the SCell is detected, the UE may use the results of the search to recover or restore the connection or communication link with the SCell. The connection is recovered or restored when the UE is able to establish communication with the detected SCell to a quality level that decoding may occur of data received via the SCell. In some circumstances, the SCell recovered or restored may be the same SCell associated with the failure event. In other circumstances, the SCell recovered may, in fact, be a new SCell that was activated when the UE was out of range of that SCell's coverage area. The UE may use the results from the search to initialize or re-initialize the time/frequency tracking loops of the recovered SCell.

FIG. 3 is a block diagram illustrating a wireless network 30 serving a UE 300 configured according to one aspect of the present disclosure and including a radio link status component 330. The UE 300 may be an example of a UE 120 in FIG. 1 and FIG. 2. The radio link status component 330 may perform radio link monitoring operations at the UE 300. In particular, the radio link status component 330 may monitor the radio link between the UE 300 and an SCell. The radio link status component 330 may include a monitoring component 332 for monitoring a downlink radio link quality of a SCell in unlicensed spectrum, an analysis component 334 for detecting a first event based on the downlink radio link quality, a failure state component 336 for declaring a failure state of the secondary cell in response to detecting the first event, and a link recovery component 338 for recovering from a failure state.

At time, t1, UE 300 is in communication with eNB 301, within coverage area 31, and remote radio head (RRH) 302, within coverage area 32. Wireless network 30 is configured to use carrier aggregation. UE 300 communicates using the primary component carrier through the PCell, eNB 301. Wireless network 30 assigns and activates RRH 302 to communicate over the secondary component carrier as an SCell to UE 300. At time, t1, UE 300 is communicating with the PCell eNB 301 and is also decoding communication on the secondary component carrier from SCell RRH 302. Also at time, t1, wireless network 30 assigns and activates access point 303 as an SCell for UE 300. UE 300 may or may not be informed of this assignment of access point 303. However, at time, t1, UE 300 is not within coverage area 33 of access point 303. Thus, as UE 300 fails to detect access point 303, it reports this failure to wireless network 30 through PCell eNB 301, such as through a low or 0 CQI or out-of-range CQI indication and/or a low value for a rank indicator. In an aspect, however, the failure to detect access point 303 may also be due to the access point 303 muting sub-frames for carrier sense adaptive transmission (CSAT). Further details of CSAT are provided below in connection with FIGS. 9-11. Accordingly, a single determination or transmission of a low or 0 CQI or out-of-range QCI indication and/or low value for a rank indicator may not be indicative of overall link quality. Accordingly, the UE 300 may monitor the determined CQI values for repeated 0 CQI or out-of-range CQI indication and/or low values for the rank indicator. Conversely, the UE may monitor for a non-zero CQI during a time period to determine that no failure has occurred.

At time, t2, UE 300 has traveled into coverage area 33 of SCell access point 303 and out of coverage area 32 of SCell RRH 302. UE 300 monitors the link quality of the connection or communication link with SCell RRH 302. When a failure event is detected, UE 300 declares for itself a failure state with SCell RRH 302. This failure event may be detected by periodically performing a narrowband cell search for the SCell RRH 302, counting non-muted subframes from the SCell RRH 302 within a time period, monitoring determined CQI values for the SCell RRH 302 during a time period, or monitoring an SNR metric associated with the SCell, such as SCell RRH 302. In response to the failure state, UE 300 may modify operations by suspending or deactivating certain components and/or operations associated with the connection to SCell RRH 302, such as reducing power to the receive and transmit paths, suspending the demodulation path with SCell RRH 302, and the like. UE 300 may also begin a cell search for SCell RRH 302 in response to the failure state being declared.

Regarding SCell access point 303, access point 303 may be activated by wireless network 30 as an SCell for UE 300 at time, t1. However, upon activation of SCell access point 303, UE 300 may not be within coverage area 33 of SCell access point 303. When UE 300 enters coverage area 33 of SCell access point 303, UE 300 may begin to detect the PSS/SSS of SCell access point 303 in a cell search. UE 300 may then initialize the time/frequency tracking loops and establish a connection with SCell access point 303 at time, t2. Once the connection is established, UE 300 may unsuspend or activate the components and/or operations that were associated with the connection of SCell RRH 302 and may begin reporting a CQI to wireless network 30 for SCell access point 303, after which wireless network 30 may begin transmitting data to UE 300 over the secondary component carrier through SCell access point 303, thus, providing additional bandwidth to UE 300.

It should be noted that SCell access point 303 may be detected during the cell search that begins when the failure state is declared on the failure of the connection with SCell RRH 302 or during any periodic cell search. In such case of detecting a new secondary cell, UE 300 may compare the time/frequency offset data recovered from the cell search against the prior time/frequency offset data maintained by the previous time/frequency tracking loops associated with SCell RRH 302. During normal connection with a secondary cell, a UE may monitor the time/frequency offset data associated with the time/frequency tracking loops. The UE may maintain this time/frequency offset data when the connection is lost and this offset data will be compared against the search values of time/frequency offsets when the secondary cell is again detected. If the difference between the previous value of time/frequency offsets and the search values is small or, at least within the pull-in range of the time/frequency tracking loop, then the tracking loops may not be re-initialized. However, when offset values are out-of-sync by an amount outside of the pull-in range of the tracking loops, UE 300 may repopulate the time/frequency offset data to the tracking loops using the offset data resulting from the cell search.

At time, t3, UE 300 may move back into coverage area 32 of SCell RRH 302, while staying within coverage areas 32 and 31 of SCell access point 303 and PCell eNB 301, respectively. UE 300 may continue searching for available SCells. As UE 300 initially re-enters coverage area 32 of SCell RRH 302, the cell search will detect the PSS/SSS from SCell RRH 302 and, when the signal quality of the reference signals from SCell RRH 302 becomes strong enough to meet certain detectability criteria, e.g., the synchronization signal (PSS/SSS) has an SNR above a certain threshold or has a reference signal receive power (RSRP) above a certain other threshold, UE 300 may initialize the time/frequency tracking loops using the time/frequency offset information from the cell search for SCell RRH 302. UE 300 may also begin transmitting CQI information to wireless network 30 through PCell eNB 301. Wireless network 30 may then be able to increase the bandwidth available to UE 300 by sending data through the secondary component carrier used by SCell RRH 302 in addition to SCell access point 303.

FIG. 4 is a functional block diagram illustrating an example method 400 including example blocks executed to implement one aspect of the present disclosure. At block 410, the method 400 may include monitoring a downlink radio link quality of a secondary cell operating in unlicensed spectrum at a mobile device for an event indicating failure of a communication link over the secondary component carrier in the unlicensed spectrum with the secondary cell. In an aspect, for example, the monitoring component 332 of the UE 300 may monitor the downlink radio link quality of a secondary cell (e.g., SCell access point 303) operating in unlicensed spectrum for an event that indicates failure of the communication link over the secondary component carrier in the unlicensed spectrum with the secondary cell. The monitoring component 332 may perform the monitoring by various means, such as by periodically performing a narrowband cell search for the secondary cell, counting non-muted sub-frames from the secondary cell within a time period, monitoring determined CQI values for the secondary cell during a time period, or monitoring an SNR metric associated with the secondary cell, and the like. For example, in an aspect, the monitoring component 332 may perform periodic cell searches for the PSS/SSS of the secondary cell. These cell searches may be configured as narrowband searches in order to detect the synchronization signals of the secondary cells, such as the PSS and SSS.

In block 420, the method 400 may include detecting a first event based on the downlink radio link quality. In an aspect, for example, the analysis component 334 of the UE 300 may detect the first event based on the downlink radio link quality. For example, the analysis component 334 may determine that a failure event has occurred when the monitoring component 332 detects a threshold number of consecutive search failures (e.g., searches where the PSS/SSS is not detected). The threshold may be a configurable number greater than or equal to two that indicating that the SCell is unavailable for a significant portion of time. A low threshold number may conserve resources by triggering a failure state for the secondary cell, but may also prevent use of a secondary cell that provides a number of opportunistic transmission opportunities. In an aspect five consecutive search failures may indicate a low availability of the SCell suggesting a link failure event.

As another example, in an aspect, in block 410, the monitoring component 332 may count a number of non-muted sub-frames received during a most recent time period or number of sub-frames. The monitoring component 332 may determine whether each sub-frame is received based on an SNR of the CRS for the secondary cell. In block 420, when the number of sub-frames received during a time period is less than a threshold number of sub-frames, the analysis component 334 may determine that a failure event has occurred. In an aspect, the threshold may be based on a false detection rate for the CRS. For example, if due to random errors, the UE falsely detects the CRS 1% of the time, the UE may determine that a failure event has occurred when the UE detects a CRS in less than 2% (indicating that about half of the detected sub-frames are false detections) of the sub-frames within a most recent time period.

As another example, in an aspect, the monitoring component 332 may monitor determined CQI values in block 40. The UE 300 may include reported CQI values as well as values that are not reported, for example, when the UE has no uplink data. Rather than looking for a single low CQI value, which may be the result of a muted sub-frame, the analysis component 334 may check for a threshold time period having no determined CQI with a non-zero value. If no non-zero CQI is determined during a time period, the analysis component 334 may determine that a failure event has occurred. The time period may be configurable. A time period on the order of 1000 ms may be sufficient to detect a failure event.

As another example, in an aspect, the monitoring component 332 may monitor determined SNR values in block 410. Rather than looking for a single low SNR value, which may be the result of a muted sub-frame, the analysis component 334 may check for a threshold time period having no determined SNR with a value less than an SNR threshold. For example, the SNR threshold may be an SNR necessary for meeting a minimum data rate (e.g., based on a modulation and coding scheme) that justifies the cost of monitoring the secondary cell. If the determined SNR remains less than the SNR threshold during a time period, the UE may determine that a failure event has occurred. Once again, a time period on the order of 1000 ms may be sufficient to detect a failure event.

Additionally, any of the above failure events may be combined with any of the other failure events. For example, the UE may monitor for all of the failure events and declare a local radio link failure when at least two failure events have occurred. Accordingly, the method 400 may optionally include detecting a second failure event, detecting a third failure event, and so on. In another aspect, one or more of the failure events may be considered mandatory while other failure events are considered optional. For example, a UE may require one mandatory failure event and another one of a plurality of other failure events to occur. Additionally, various thresholds may be set for the same failure event such that, for example, a failure event based on a low level threshold may require a second failure event whereas a similar failure event based on a higher level threshold may automatically trigger declaring a local radio link failure. The UE may use logic operations to combine the failure events.

At block 430, the method 400 may include declaring a failure state of the secondary cell in response to detecting the first event. During the failure state, the mobile device may adjust operation related to the secondary component carrier. In an aspect, for example, the failure state component 336 may declare a failure state of the secondary cell in response to detecting the first event. For example, when the analysis component 334 detects a failure event in the connection or communication link with the secondary cell, the failure state component 336 may adjust various operations related to communication using the secondary component carrier. For example, the failure state component 336 may suspend or reduce the power or frequency of various components and resources associated with the secondary cell communication with the failed communication link, such as the RF chip state, the transmit and receive path states, the device voltage levels, memory usage, various components' operating frequencies, and the like. The failure state component 336 may also suspend or deactivate the demodulation path associated with the failed secondary cell communication link. Thus, in response to the failure event detection, the failure state component 336 may adjust communications operations to save power and resources.

In addition to deactivating various communications operations on detection of a failure event, the UE may optionally attempt to recover a secondary connection. At block 440, the method 400 may optionally include performing a cell search on the secondary component carrier in response to the failure state. For example, the UE 300 may begin monitoring the periodic search results on secondary component carriers to check whether the secondary cell is found that meets certain detectability criteria, e.g., the synchronization signal (PSS/SSS) has an SNR above a certain threshold or has a RSRP above a certain other threshold for adequate communication. For example, the failure state component 336 may control the monitoring component 332 to perform these cell searches. These cell searches may be configured as narrowband searches in order to detect the synchronization signals of the secondary cells, such as the PSS and SSS. The UE may also begin maintenance of the failure state with the wireless network by transmitting 0 CQI, signaling a rank indicator of 1 for the secondary cell, and, in case of cross-carrier scheduling, the UE may cease signaling acknowledgements (ACKs) or negative ACKs (NACKs) for the downlink schedules of the secondary cell.

At block 450, the method 400 may optionally include recovering the communication link over the secondary component carrier with one or more configured secondary cells based on signal quality during the cell search. In an aspect, for example, the link recovery component 338 may recover the communication link over the secondary component carrier with the one or more configured secondary cells based on signal quality during the cell search. For example, when one or more suitable configured secondary cells is detected during the optional cell search performed at block 440, the results from the search, such as the time/frequency offsets, and the like, may be used to recover the communication link over the secondary component carrier with the one or more configured secondary cells. The configured secondary cells may include the secondary cell with which the previous communication link was lost, or it may be a different secondary cell enabled by the network that is detected and meets the appropriate threshold quality measurements for establishing communication. On detection, the link recovery component 338 may update any secondary cell tracking loops using the offset data resulting from the cell search. This information may be used to initialize or re-initialize the tracking loops for the one or more configured secondary cells. Also upon detection of the one or more configured secondary cells, the link recovery component 338 may activate any suspended or deactivated components or functionality that were suspended during the declared failure state, such as the demodulation path, transmit and receive paths, and the like.

FIG. 5 is a timing diagram 500 illustrating an example of the operation of the UE 300 according to one aspect of the present disclosure. UE 300 may operate in a wireless network that uses carrier aggregation including a secondary component carrier in unlicensed spectrum. At time 501, the wireless network may configure the carrier aggregation, establishing the primary and secondary component carriers for UE 300. At time 502, the wireless network may assign and may activate each of the SCells that will provide the secondary component carriers for UE 300. After activation of the SCells, UE 300 may establish a good communication link with at least one of the SCells activated. Accordingly, after time 502, UE 300 may begin reporting CQI for the connected SCell and may receive and demodulate data from this SCell, while maintaining the primary component carrier connection with the serving PCell. At time 503, UE 300 may detect a failure event with the communication link with at least one of the connected SCells.

In response to detecting the failure event, UE 300, at time 503, may declare a failure state with regard to the SCell and may modify various operations associated with secondary component carrier communication with the failed SCell, including suspending or reducing power to the SCell transmit and receive paths, the demodulation path, changing the operating frequency of various components, and the like. In response to declaring the failure state, UE 300 may also perform a narrowband search for the failed SCell link by monitoring the periodic search results on the secondary component carrier to check whether the SCell is found and meets certain detectability criteria, e.g., the synchronization signal (PSS/SSS) has an SNR above a certain threshold or has a RSRP above a certain other threshold.

During period 504, UE 300 may operate in a reduced power/resource utilization state and may perform the narrowband cell search for the failed SCell link. At time 505, UE 300 may again detect the SCell through the cell search. In response to detecting the SCell again, the suspended components and/or operations may be reactivated for managing the connection with the SCell. UE 300, thus, may begin reporting CQI for the SCell and receiving and decoding data from the SCell.

FIG. 6 is a block diagram illustrating a UE 300 configured according to one aspect of the present disclosure. UE 300 may include the controller/processor 280 (see FIG. 2). Controller/processor 280 may control the components and may execute logic stored in memory 282 (see FIG. 2) that provides the features of functionalities of UE 300 including the features and functionalities of radio link status component 330. For example, the radio link status component 330 may include logic stored in memory 282. In order to monitor the communication link with the connected SCell, UE 300, under control of controller/processor 280, may control the signals received through the SCell demodulation path 603 of wireless radios 604, from the connected SCell. The combination of these components and acts may provide means for monitoring a downlink radio link quality of one or more secondary cells at a mobile device for an event indicating failure of a communication link with at least one of the one or more secondary cells.

Controller/processor 280 may access memory 282 to execute link analysis logic 600. The executing environment of link analysis logic 600, may analyze the connection with the SCell and may determine whether a link failure has occurred. For example, the executing link analysis logic 600 may cause controller/processor 280 to periodically execute cell search logic 607 in memory 282 to perform a cell search for the active SCell link by monitoring the periodic search results on the secondary component carrier to check whether the SCell is found. UE 300 may receive the search results after executing cell search logic 607, under control of controller/processor 280, and receiving and sending search signals through SCell transmit path 602 and SCell demodulation path 603, respectively, in wireless radios 604. The controller/processor 280 may declare a failure event when the SCell is not found in the periodic search results for a threshold number of consecutive searches.

Alternatively, the executing link analysis logic 600 may cause controller/processor 280 to detect the failure event when a number of sub-frames successfully received is less than a threshold number of sub-frames. The SCell demod path 603 may determine whether a sub-frame is successfully received based on whether a CRS of the SCell is detected in the sub-frame.

In another aspect, the executing link analysis logic 600 may cause the controller/processor 280 to monitor a channel quality indication (CQI) determined by the SCell demodulation path 603 and detect the failure event when no CQI value greater than 0 is determined during a time period.

In another aspect, the executing link analysis logic 600 may cause controller/processor 280 to determine the SNR of the SCell signal received at wireless radios 604 through SCell demodulation path 603 and when the SNR remains below a predetermined threshold for a certain period of time, the UE 300 may declare the failure state.

Based on the results of the executing link analysis logic 600, controller/processor 280 may detect a failure of the communication link with the SCell and may declare a failure state. In response, to the declared failure state, UE 300, under control of controller/processor 280, may suspend or deactivate SCell transmit path 602 and SCell demodulation path 603 in wireless radios 604. Controller/processor 280 may also reduce the power output of power supply 605 in order to reduce the voltage level to wireless radios 604, and the like. Moreover, controller/processor 280 may change the frequency of various components by changing the operations of frequency generator 606. The combination of these components and acts may provide means for declaring a failure state on the at least one of the one or more secondary cells in response to detecting the event, during which mobile device may adjust operation related to the secondary component carrier

Also, in response to the declared failure state, controller/processor 280 may execute cell search logic 607 in memory 282 to perform a cell search for the failed SCell link by monitoring the periodic search results on the secondary component carrier to check whether the SCell is found and meets certain detectability criteria, e.g., the synchronization signal (PSS/SSS) has an SNR above a certain threshold or has a RSRP above a certain other threshold. The executing cell search logic 607 sends search messages and listens for synchronization signals over wireless radios 604. The combination of these components and acts may provide means for performing cell search for the at least one of the one or more secondary cells in response to the failure state.

During the declared failure state, UE 300 may also begin transmitting a low, e.g., a 0, CQI and signaling a low, e.g., a 1, rank indicator for the SCell to the network. In case of cross-carrier scheduling, UE 300 may also cease signaling acknowledgements (ACKs) or negative ACKs (NACKs) for the downlink schedules of the SCell.

When the SCell is detected by UE 300, through execution of cell search logic 607 by controller/processor 280, controller/processor 280 may reactivate each of the components and processes that were suspended during the failure state. Controller/processor 280 may reactivate SCell transmit path 602 and SCell demodulation path 603, and may return the power and frequency settings back to the original levels through access to power supply 605 and frequency generator 606. Controller/processor 280 may compare the time/frequency offsets that resulted from execution of cell search logic 607 to the operation of SCell tracking loops 601 operated from SCell demodulation path 603 by controller/processor 280. If the time/frequency offsets determined in the cell search do not match the time/frequency offsets of the operating SCell tracking loops 601, and the difference is greater than the pull-in range of the operating SCell tracking loops 601, then controller/processor 280 may initialize or re-initialize SCell tracking loops 601 using the time/frequency offsets from execution of cell search logic 607. UE 300, under control of controller/processor 280 may then be able to recover or reestablish the connection with the detected SCell. UE 300 may begin transmitting CQI for the recovered SCell to the network and may begin to receive data transmitted over the SCell to increase the throughput from the network. The combination of these components and acts may provide means for recovering the communication link with a secondary cell detected during the cell search. Referring to FIG. 7, one or more components of UE 300 of FIG. 3, by which radio link monitoring of secondary cells in unlicensed spectrum may be implemented according to an aspect of the disclosure, are illustrated with respect to radio link status component 330. It should be noted that each of the one or more components of UE 300 may be implemented as software, hardware, firmware, or any combination thereof. As noted above, UE 300 generally operates radio link status component 330 to monitor the status of communication link 136 and to declare a failure state when a failure event is detected such that the UE 300 may consume less power.

According to the present aspects, the UE 300 may include one or more processors 733 that may operate in combination with the radio link status component 330 configured to monitor the status of communication link 136 and to declare a failure state when a failure event is detected. For example, the processors 733 may include the controller/processor 280 of FIG. 2 and FIG. 6. The radio link status component 330 may be communicatively coupled to a transceiver 740, which may include a receiver 742 for receiving and processing RF signals and a transmitter 744 for processing and transmitting RF signals. The processor 733 may be coupled to the transceiver 740 and a memory 730 via at least one bus 760. The memory 730 may correspond to the memory 282 in FIG. 2 and FIG. 6.

The receiver 742 may include hardware, firmware, and/or software code executable by a processor for receiving data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium). The receiver 742 may be, for example, a radio frequency (RF) receiver. In an aspect, the receiver 742 may receive signals transmitted by one or more of the eNBs 110. In an aspect, the receiver 742 may be configured to receive signals from the eNB 110 as a secondary cell.

The transmitter 744 may include hardware, firmware, and/or software code executable by a processor for transmitting data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium). The transmitter 744 may be, for example, a RF transmitter. The transmitter 744 may transmit information regarding the communication link 136 such as a CQI.

In an aspect, the one or more processors 733 can include a modem 738 that uses one or more modem processors. The various functions related to radio link status component 330 may be included in modem 738 and/or processors 733 and, in an aspect, can be executed by a single processor, while in other aspects, different ones of the functions may be executed by a combination of two or more different processors. For example, in an aspect, the one or more processors 733 may include any one or any combination of a modem processor, or a baseband processor, or a digital signal processor, or a transmit processor, or a transceiver processor associated with transceiver 740. In particular, the one or more processors 733 may implement components included in the radio link status component 330.

Moreover, in an aspect, UE 300 may include RF front end 750, which may operate in communication with one or more antennas 720 and transceiver 740 for receiving and transmitting radio transmissions, for example, wireless communications transmitted by at least one eNB 110 or wireless transmissions transmitted by UE 300. RF front end 750 may be connected to one or more antennas 720 and can include one or more low-noise amplifiers (LNAs) 751, one or more switches 752, 753, 756, one or more power amplifiers (PAs) 755, and one or more filters 754 for transmitting and receiving RF signals. In an aspect, the wireless radios 604 and components thereof in FIG. 6 may include or may be implemented by the RF front end 750.

In an aspect, LNA 751 can amplify a received signal at a desired output level. In an aspect, each LNA 751 may have a specified minimum and maximum gain values. In an aspect, RF front end 750 may use one or more switches 752 to select a particular LNA 751 and its specified gain value based on a desired gain value for a particular application.

Further, for example, one or more PA(s) 755 may be used by RF front end 750 to amplify a signal for an RF output at a desired output power level. In an aspect, each PA 755 may have specified minimum and maximum gain values. In an aspect, RF front end 750 may use one or more switches 756 to select a particular PA 755 and its specified gain value based on a desired gain value for a particular application.

Also, for example, one or more filters 754 can be used by RF front end 750 to filter a received signal to obtain an input RF signal. Similarly, in an aspect, for example, a respective filter 754 can be used to filter an output from a respective PA 755 to produce an output signal for transmission. In an aspect, each filter 754 can be connected to a specific LNA 751 and/or PA 755. In an aspect, RF front end 750 can use one or more switches 753 to select a transmit or receive path using a specified filter 754, LNA 751, and/or PA 755, based on a configuration as specified by transceiver 740 and/or processor 733.

The monitoring component 332 may include hardware, firmware, and/or software code executable by a processor (e.g., processor(s) 733) for monitoring a downlink radio link quality of a secondary cell in unlicensed spectrum, the code comprising instructions and being stored in a memory (e.g., memory 730 or another computer-readable medium). For example, the monitoring component 332 may include or control an antenna 720, RF front end 750, and/or receiver 742 to receive signals transmitted by the eNB on communication link 136. The monitoring component 332 may monitor various properties of the communication link and may store information regarding the communication link 136 for a time period. For example, the monitoring component 332 may monitor: received sub-frames including a CRS, CQI values determined for the communication link 136, and/or SNR values determined for the communication link 136. The monitoring component 332 may also perform periodic cell searches for a synchronization signal of the eNB 110 and determine whether the synchronization signal is detected during each search.

The analysis component 334 may include hardware, firmware, and/or software code executable by a processor (e.g., processor(s) 733) for detecting a first event based on the downlink radio link quality, the code comprising instructions and being stored in a memory (e.g., memory 730 or another computer-readable medium). For example, the analysis component 334 may include configurable thresholds stored in the memory 730 and instructions executable by the processor 733 for determining when the downlink radio link quality indicates a radio link failure event.

The failure state component 336 may include hardware, firmware, and/or software code executable by a processor (e.g., processor(s) 733) for declaring a failure state of the secondary cell in response to detecting the first event, during which the UE 300 adjusts operation related to the secondary component carrier in the unlicensed spectrum, the code comprising instructions and being stored in a memory (e.g., memory 730 or another computer-readable medium). In an aspect, the failure state component 336 may control various components of the UE 300 to reduce power consumption during the failure state. For example, the failure state component 335 may control the antenna 720, RF front end 750, and/or receiver 742 to stop attempting to receive or decode signals transmitted by the eNB on communication link 136 during the failure state.

The link recovery component 338 may include hardware, firmware, and/or software code executable by a processor (e.g., processor(s) 733) for attempting to recover from a radio link failure state, the code comprising instructions and being stored in a memory (e.g., memory 730 or another computer-readable medium). For example, the link recovery component 338 may control the antenna 720, RF front end 750, and/or receiver 742 to perform a cell search for the failed SCell link by monitoring the periodic search results on the secondary component carrier to check whether the SCell is found and meets certain detectability criteria. The link recovery component 338 may then reactivate the SCell and end the failure state of the secondary cell.

FIG. 8 illustrates a conceptual diagram 800 showing an example of carrier aggregation using a component carrier in unlicensed spectrum. For example, the UE 300 may perform carrier aggregation. In an aspect, unlicensed spectrum may refer to a portion of frequency spectrum that is not licensed (e.g., by a regulatory agency such as the Federal Communications Commission (FCC)) to a particular licensee. For example, a large portion (e.g., >400 MHz) of spectrum may be available in a 5 GHz band while another portion of unlicensed spectrum may be available in a 2.4 GHz band. In an aspect, other radio access technologies (e.g., Wi-Fi) may also use the unlicensed spectrum. As illustrated in FIG. 8, LTE in unlicensed spectrum may utilize a primary component carrier in licensed spectrum and a secondary component carrier in unlicensed spectrum. The primary component carrier may be an LTE-Advanced anchor that provides for mobility and other signaling. A network source 810 such as a packet data network gateway may provide downlink data to PCell 820 for transmission over the primary component carrier 822 and to an SCell 830 for transmission over the secondary component carrier 832. The UE 300 including a radio link status component 330 may aggregate the bandwidth of the component carriers at the media access control (MAC) layer to increase throughput. The radio link status component 330 may monitor the status of the communication link on the secondary component carrier 832, which may be in unlicensed spectrum. LTE in unlicensed spectrum may include features for coexistence with neighbor systems such as Wi-Fi.

FIG. 9 illustrates a timing diagram 900 showing an example of carrier sense adaptive transmission (CSAT) for use in unlicensed spectrum. CSAT is a mechanism to reduce co-channel interference from LTE in unlicensed spectrum to Wi-Fi. CSAT may be implemented when no free channel (not used by Wi-Fi) is available. CSAT may create a time division multiplex (TDM) transmission pattern on an SCell with a cycle, T_(CSAT) 910. As illustrated in FIG. 9, a MAC control element at an eNB may use fast activation/deactivation to switch the SCell between an on period (T_(ON)) 920 and an off period (T_(OFF)) 930. The SCell may obtain measurement during the T_(OFF) 930 of Wi-Fi medium utilization. The SCell may use a co-located Wi-Fi access point to sniff the medium using preamble detection for Wi-Fi activity. The T_(CSAT) or the T_(ON) and T_(OFF) periods may be adjusted based on the Wi-Fi activity. As discussed above, when CSAT is implemented, the UE may have difficulty monitoring radio link quality because it may difficult to determine whether the sub-frame was muted or the radio link was poor quality. The radio link failure events discussed above, however, may be accurately detected even when the UE is unsure of whether a sub-frame was muted.

FIG. 10 illustrates a timing diagram 1000 showing an example of an enhanced CSAT (eCSAT) system that may operate without a clear channel assessment (CCA) or listen before talk (LBT) procedure. The eNB may activate UEs with downlink data via an activation MAC control element (CE) command and may deactivate UEs without downlink data via a deactivation MAC CE command to form an outer loop control 1010. The eNB may run an inner activation/deactivation cycle by turning the CRS on or off. The UE may assume the cell is on when CRS is present in a sub-frame. The UE may assume the cell is off when CRS is not present in the subframe. When in an OFF-state, the SCell may cease all transmissions including PSS/SSS, scheduling information (SI) signals, CRS signals, etc. A continuous on duration may be expected to be shorter than the T_(ON) in CSAT. For example, the on duration (T_(on)) 1020 may be approximately 4 ms, although 1 ms is theoretically possible. As illustrated in FIG. 10, the UE may activate the outer loop control 1010 on the 8^(th) sub-frame after the activation command sub-frame and the SCell may start a duty cycle including an on/off pattern for that UE. The SCell may maintain the duty cycle based on observation of channel activity. The UE may stop monitoring downlink sub-frames after receiving the deactivation command.

In an aspect, the eNB may also transmit a discovery reference signal (DRS) 1030, which may include physical layer signals such as a primary synchronization signal (PSS), secondary synchronization signal (SSS), and a cell specific reference signal (CRS). As illustrated in FIG. 10, the DRS 1030 may not be time aligned with the T_(ON) period. Accordingly, the DRS and component signals may be muted. Because the UE may detect the state of the SCell based on the CRS signals, monitoring radio link quality may be difficult because it may be unclear whether CRS in a sub-frame was intentionally muted or whether the quality of the CRS was poor. Once again, the radio link failure events discussed above may be accurately detected even when the UE is unsure of whether a sub-frame was muted.

FIG. 11 illustrates a timing diagram 1100 showing an example of eCSAT operation with a CCA or LBT procedure. The eCSAT operation may operate as in FIG. 10, but the SCell may also perform a CCA operation 1110 before the inner activation to turn the CRS on. The CCA operation may ensure that the channel is clear of Wi-Fi or other transmissions before an LTE transmission begins. Further, the SCell may transmit a clear to send to self (CTS2S) message 1120 immediately following the CCA operation. The CTS2S transmission may silence Wi-Fi systems for a duration. The eCSAT operation, however, may not provide certainty at the UE as to whether CRS in a sub-frame was intentionally muted or whether the quality of the CRS was poor. Once again, the radio link failure events discussed above may be accurately detected even when the UE is unsure of whether a sub-frame was muted.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The functional blocks and modules in FIG. 4 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. Skilled artisans will also readily recognize that the order or combination of components, methods, or interactions that are described herein are merely examples and that the components, methods, or interactions of the various aspects of the present disclosure may be combined or performed in ways other than those illustrated and described herein.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. A computer-readable storage medium may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, non-transitory connections may properly be included within the definition of computer-readable medium. For example, if the instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, or digital subscriber line (DSL), then the coaxial cable, fiber optic cable, twisted pair, or DSL are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

What is claimed is:
 1. A method for wireless communication on a secondary component carrier in unlicensed spectrum in a wireless communication network using carrier aggregation, comprising: monitoring a downlink radio link quality of a secondary cell in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link over the secondary component carrier in the unlicensed spectrum with the secondary cell, wherein monitoring the downlink radio link quality of the secondary cell in the unlicensed spectrum includes determining, for each of a plurality of sub-frames, whether the sub-frame includes a cell specific reference signal (CRS); detecting a first event based on the downlink radio link quality, wherein detecting the first event includes detecting the first event based on sub-frames determined to include the CRS; and declaring a failure state of the secondary cell in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.
 2. The method of claim 1, wherein monitoring the downlink radio link quality of the secondary cell includes performing a cell search for a synchronization signal of the secondary cell in the unlicensed spectrum at the mobile device, and wherein detecting the first event includes determining that the synchronization signal is not detected in a threshold number of consecutive cell searches.
 3. The method of claim 1, wherein monitoring the downlink radio link quality of the secondary cell includes determining a number of sub-frames including the CRS received from the secondary cell during a period of most recent sub-frames, and wherein detecting the first event includes determining that the number of sub-frames including the CRS is less than a threshold number of sub-frames.
 4. The method of claim 3, wherein a ratio between the threshold number of sub-frames and a number of sub-frames in the period is based on a false detection rate for the CRS.
 5. The method of claim 1, wherein monitoring the downlink radio link quality of the secondary cell includes monitoring a channel quality indication (CQI) determined by the mobile device, and wherein detecting the first event includes determining that no CQI value greater than 0 is determined during a time period.
 6. The method of claim 1, wherein monitoring the downlink radio link quality of the secondary cell includes monitoring a signal-to-noise ratio (SNR) value at the mobile device, and wherein detecting the first event includes determining that the SNR value does not exceed a threshold value during a time period.
 7. The method of claim 1, further comprising: detecting a second event based on the downlink radio link quality, wherein declaring the failure state of the secondary cell is in response to detecting both the first event and the second event.
 8. The method of claim 7, wherein the first event is a mandatory event and the second event is one of two or more optional events.
 9. An apparatus for wireless communication on a secondary component carrier in unlicensed spectrum in a wireless communication network using carrier aggregation, the apparatus comprising: at least one processor; and a memory coupled to the at least one processor, wherein the at least one processor is configured to: monitor a downlink radio link quality of a secondary cell operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link over the secondary component carrier with the secondary cell by determining, for each of a plurality of sub-frames, whether the sub-frame includes a cell specific reference signal (CRS); detect a first event based on the downlink radio link quality of sub-frames determined to include the CRS; and declare a failure state of the secondary cell in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.
 10. The apparatus of claim 9, wherein the at least one processor is configured to monitor the downlink radio link quality of the secondary cell in the unlicensed spectrum by performing a cell search for a synchronization signal of the secondary cell in the unlicensed spectrum at the mobile device, and wherein the at least one processor is configured to detect the first event when the synchronization signal is not detected in a threshold number of consecutive cell searches.
 11. The apparatus of claim 9, wherein the at least one processor is configured to monitor the downlink radio link quality of the secondary cell in the unlicensed spectrum by determining a number of sub-frames including the CRS received from the secondary cell during a period of most recent sub-frames, and wherein the at least one processor is configured to detect the first event when the number of sub-frames including the CRS is less than a threshold number of sub-frames.
 12. The apparatus of claim 11, wherein a ratio between, the threshold number of sub-frames and a number of sub-frames in the period is based on a false detection rate for the CRS.
 13. The apparatus of claim 9, wherein the at least one processor is configured to monitor the downlink radio link quality of the secondary cell in the unlicensed spectrum by monitoring a channel quality indication (CQI) determined by the mobile device, and wherein the at least one processor is configured to detect the first event when no CQI value greater than 0 is determined during a time period.
 14. The apparatus of claim 9, wherein the at least one processor is configured to monitor the downlink radio link quality of the secondary cell in the unlicensed spectrum by monitoring a signal-to-noise ratio (SNR) value at the mobile device, and wherein the at least one processor is configured to detect the first event when the SNR value does not exceed a threshold value during a time period.
 15. The apparatus of claim 9, wherein the at least one processor is configured to detect a second event based on the downlink radio link quality, and wherein the at least one processor is configured to declare the failure state of the secondary cell in response to detecting both the first event and the second event.
 16. The apparatus of claim 15, wherein the first event is a mandatory event and the second event is one of a plurality of optional events.
 17. An apparatus for wireless communication on a secondary component carrier in unlicensed spectrum in a wireless communication network using carrier aggregation, comprising: means for monitoring a downlink radio link quality of a secondary cell operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link over the secondary component carrier with the secondary cell, wherein the means for monitoring are configured to monitor the downlink radio link quality of the secondary cell in the unlicensed spectrum by determining, for each of a plurality of sub-frames, whether the sub-frame includes a cell specific reference signal (CRS); means for detecting a first event based on the downlink radio link quality, wherein the means for detecting are configured to detect the first event based on sub-frames determined to include the CRS; and means for declaring a failure state of the secondary cell in response to detecting the event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.
 18. The apparatus of claim 17, wherein the means for monitoring are configured to perform a cell search for a synchronization signal of the secondary cell in the unlicensed spectrum at the mobile device, and wherein the means for detecting are configured to detect the event when the synchronization signal is not detected in a threshold number of consecutive cell searches.
 19. The apparatus of claim 17, wherein the means for monitoring are configured to determine a number of sub-frames including the CRS received from the secondary cell during a period of most recent sub-frames, and wherein the means for detecting are configured to detect the event when the number of sub-frames including the CRS is less than a threshold number of sub-frames.
 20. The apparatus of claim 19, wherein a ratio between the threshold number of sub-frames and a number of sub-frames in the period is based on a false detection rate for the CRS.
 21. The apparatus of claim 17, wherein the means for monitoring are configured to monitor a channel quality indication (CQI) determined by the mobile device, and wherein the means for detecting are configured to detect the first event when no CQI value greater than 0 is determined during a time period.
 22. The apparatus of claim 17, wherein the means for monitoring are configured to monitor a signal-to-noise ratio (SNR) value at the mobile device, wherein the means for detecting are configured to detect the event when the SNR value does not exceed a threshold value during a time period.
 23. A non-transitory computer-readable medium storing, computer executable code for wireless communication on a secondary component carrier in unlicensed spectrum in a wireless communication network using carrier aggregation, comprising code for causing a computer to: monitor a downlink radio link quality of a secondary cell operating in the unlicensed spectrum at a mobile device for an event indicating failure of a communication link over the secondary component carrier with the secondary cell, wherein monitoring the downlink radio link quality of the secondary cell in the unlicensed spectrum includes determining, for each of a plurality of sub-frames, whether the sub-frame includes a cell specific reference signal (CRS); detect a first event based on the downlink radio link quality, wherein detecting the first event includes detecting the first event based on sub-frames determined to include the CRS; declare a failure state of the secondary cell in response to detecting the first event, during which the mobile device adjusts operation related to the secondary component carrier in the unlicensed spectrum.
 24. The non-transitory computer-readable medium of claim 23, wherein detecting the first event includes detecting one or more of: a synchronization signal is not detected in a threshold number of consecutive cell searches; a number of sub-frames including the CRS received from the secondary cell during a period of most recent sub-frames is less than a threshold number of sub-frames; no channel quality indication (CQI) value determined by the mobile device greater than 0 is determined during a time period; or a signal-to-noise ratio (SNR) value at the mobile device does not exceed a threshold value during the time period. 